Business combination, liability for installment payments and contingent consideration.

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Period of contingent consideration.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of assets acquired at the acquisition date.

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-Name Accounting Standards Codification
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-SubTopic 20
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- Definition

The amount of identifiable intangible assets recognized as of the acquisition date.

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Amount of liabilities assumed at the acquisition date.

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- Definition

Amount of contributions made by employer into fund established for purposes of making future disbursement to individual in accordance with deferred compensation arrangement.

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No definition available.

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Minimum period the individual is required to perform services to be fully vested under the deferred compensation arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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Carrying amount of finite-lived intangible assets, indefinite-lived intangible assets and goodwill. Goodwill is an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. Intangible assets are assets, not including financial assets, lacking physical substance.

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An excess of the fair value of the modified award over the fair value of the award immediately before the modification.

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Gross value of stock (or other type of equity) issued during the period as a result of any equity-based compensation plan other than an employee stock ownership plan (ESOP). Stock issued could result from the issuance of restricted stock, the exercise of stock options, stock issued under employee stock purchase plans, and/or other employee benefit plans.

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Acquisitions (Narrative) (Details) - USD ($) $ in Thousands					12 Months Ended
Acquisitions (Narrative) (Details) - USD ($) $ in Thousands	Jan. 03, 2017	May 03, 2016	Jan. 04, 2016	Jun. 05, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 04, 2015
Business Acquisition [Line Items]
Goodwill					$ 968,834	$ 962,282
Restricted stock units, charges at the date of modification					55,900
Restricted Stock Units (RSUs) [Member]
Business Acquisition [Line Items]
Restricted stock units, charges at the date of modification						58,600
City Securities Corporation [Member]
Business Acquisition [Line Items]
Goodwill	$ 7,100
Identifiable intangible assets	$ 4,100
Period of contingent consideration	2 years
Liability for earn-out payments					500
ISM Capital LLP [Member]
Business Acquisition [Line Items]
Goodwill		$ 6,300
Identifiable intangible assets		$ 2,300
Period of contingent consideration		3 years
Liability for earn-out payments					1,900	3,700
Eaton Partners [Member]
Business Acquisition [Line Items]
Goodwill			$ 72,000
Identifiable intangible assets			$ 32,300
Period of contingent consideration			4 years
Liability for earn-out payments					$ 31,200	$ 27,300
Barclays Wealth and Investment Management, Americas [Member]
Business Acquisition [Line Items]
Goodwill							$ 24,800
Deferred consideration, recognized as a liability							15,200
Barclays Wealth and Investment Management, Americas [Member] \| Customer Relationships [Member]
Business Acquisition [Line Items]
Identifiable intangible assets							7,300
Barclays Wealth and Investment Management, Americas [Member] \| Stifel Bank [Member]
Business Acquisition [Line Items]
Loans acquired in acquisition							$ 600,000
Sterne Agee Group, Inc. [Member]
Business Acquisition [Line Items]
Goodwill and intangible assets				$ 60,800
Fair value of awards issued as retention				23,800
Employee retention compensation paid in notes				$ 33,800
Sterne Agee Group, Inc. [Member] \| Minimum [Member]
Business Acquisition [Line Items]
Individual compensation and benefits useful period				5 years
Sterne Agee Group, Inc. [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Individual compensation and benefits useful period				10 years
Sterne Agee Group, Inc. [Member] \| Customer Relationships [Member]
Business Acquisition [Line Items]
Identifiable intangible assets				$ 29,300